Interleukin-10 (IL-10) is thought to play an important role in the regulation of microbial immunity. While T-cell-derived
IL-10 has been shown to suppress cell-mediated immunity, there has been debate as to whether antigen presenting cell (APC)-derived
cytokine can perform the same function in vivo. To assess the influence of APC-produced
IL-10 on host resistance to mycobacterial
infection, transgenic mice expressing human
IL-10 under the control of the major histocompatibility complex class II promoter (hu10Tg) were infected with Mycobacterium avium, and bacterial burdens and immune responses were compared with those observed in wild-type (wt) animals. Hu10Tg mice harbored substantially higher numbers of M. avium and succumbed 16 to 18 weeks postinfection. The
granulomas in infected hu10Tg mice showed marked increases in both
acid-fast bacilli and host macrophages. In addition, these animals displayed a dramatic increase in hepatic
fibrosis. The increased susceptibility of the hu10Tg mice to M. avium
infection is independent of T-cell-produced endogenous murine
IL-10, since bacterial burdens in mice derived by crossing hu10Tg mice with murine IL-10-deficient mice were not significantly different from those in hu10Tg mice. Importantly,
gamma interferon (IFN-gamma) responses were not decreased in the infected transgenic animals from those in wt animals, suggesting the normal development of Th1 effector cells. In contrast, mycobacterium-induced macrophage apoptosis as well as production of TNF,
nitric oxide, and
IL-12p40 were strongly inhibited in hu10Tg mice. Together, these data indicate that APC-derived
IL-10 can exert a major inhibitory effect on control of mycobacterial
infection by a mechanism involving the suppression of macrophage effector function and apoptosis.